<?php
$a = '10';
$key = 'ahsfuiyeajfasdf';
echo '价格：'.$a;

?>
<form method="post" action="aa.php">
<input type="hidden" name="pa" value="<?php echo $a;?>">
<input type="hidden" name="pkey" value="<?php echo md5($a.$b.$key);?>">
<input type="submit">
</form>